Is it Rule 21.4 or 21.4a that makes the Leap Frog illegal? From what I am reading, 21.4 refers to 21.1, but 21.1 only mentions a pinned ball, not a stopped ball.
Also, it seems that 21.4a refers to 21.2a , but 21.2a only mentions if the ball is caught by the next rod, not struck.
21.4 applies 21.1 (including subsections) to 2- to 5-bar passing. This includes all of 21.1 (21.1, 21.1a, 21.1b).
21.1a and b prevent passing a ball that has been adjusted or stopped (adjusted = touched by front or back of a man).
21.2b gives the definition of a pass, which includes a ball that is quick-shot.
FWIW, I'm a certified ref. I can absolutely guarantee you that if you tried an adjustment pass from the 2-bar to the 5-bar on tour, it'd be ruled illegal (even if you quick-shot instead of catching the ball) whether it happened above or below the rod.
The rules are also heavily dependent on precedent (much like the law or the rules in, say, the NBA--travelling, for instance). So it can be difficult to get a good grasp for what the actual rules are just from reading the book. Which really sucks, and I've lobbied for a while to get a set of official interpretations published, but it's the current state of the world. Just as one instance, although 21.4a only mentions 2- to 5-bar passing, the same rule applies to goalie-rod to 5-rod passing. That's not written anywhere, but it's the official ruling. In general, if you don't have access to official rulings you should be more interested in following the intent of the rules than the slavish written word if the two are obviously in conflict.